Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors.

https://www.mdpi.com/1424-8220/9/5/3491/pdf?view=inline

Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

Techniques have been developed for the synthesis of pulse shapes using fast digital schemes in place of the traditional analog methods of pulse shaping. Efficient recursive algorithms have been developed that allow real time implementation of a shaper that can produce either trapezoidal or triangular pulse shapes. Other recursive techniques are presented which allow a synthesis of finite cusp-like shapes. Preliminary experimental tests show potential advantages of using these techniques in high resolution, high count rate pulse spectroscopy.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/31506/0000428.pdf?sequence=1

Digital synthesis of pulse shapes in real time for high resolution radiation spectroscopy

Recursive algorithms for real-time digital pulse shaping in pulse height measurements have been developed. The differentiated signal from the preamplifier (exponential pulse) is amplified and then digitized. Digital data are deconvolved so that the response of the high-pass network is eliminated. The deconvolved pulse is processed by a time-invariant digital filter which allows trapezoidal/triangular or cusp-like shapes to be synthesized. A prototype of a digital trapezoidal processor was built which is capable of sampling and processing digital data in real time at clock rates up to 50 MHz.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/31113/0000009.pdf

Digital techniques for real-time pulse shaping in radiation measurements

The Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) is a new generation high-resolution γ - ray spectrometer consisting of electrically segmented high-purity germanium crystals. GRETINA is capable of reconstructing the energy and position of each γ - ray interaction point inside the crystal with high resolution. This enables γ - ray energy tracking which in turn provides an array with large photopeak efficiency, high resolution and good peak-to-total ratio. GRETINA is used for nuclear structure studies with demanding γ - ray detection requirements and it is suitable for experiments with radioactive-ion beams with high recoil velocities. The GRETINA array has a 1 π solid angle coverage and constitutes the first stage towards the full 4 π array GRETA. We present in this paper the main parts and the performance of the GRETINA system.

The performance of the Gamma-Ray Energy Tracking In-beam Nuclear Array GRETINA

We report on an improved measurement of the 2νββ half-life of ^(136)Xe performed by EXO-200. The use of a large and homogeneous time-projection chamber allows for the precise estimate of the fiducial mass used for the measurement, resulting in a small systematic uncertainty. We also discuss in detail the data-analysis methods used for double-β decay searches with EXO-200, while emphasizing those directly related to the present measurement. The ^(136)Xe 2νββ half-life is found to be T^(2νββ)_(1/2) = 2.165±0.016(stat)±0.059(sys)×10^(21) yr. This is the most precisely measured half-life of any 2νββ decay to date.

Improved measurement of the 2νββ half-life of 136 Xe with the EXO-200 detector

A small, lightweight, and low power, spacecraft instrument, CEASE, has been designed to measure the local space radiation environment. The instrument's on-board processing algorithms use the collected data to generate warnings of the space environment hazards of radiation damage, dielectric charging and single event effects (SEE). In addition, CEASE can provide detailed space environment data to aid in analysis of anomalies that may occur on the host spacecraft.

Compact environmental anomaly sensor (CEASE): a novel spacecraft instrument for in situ measurements of environmental conditions

A digital pulse processor with improved differential linearity and reduced dead time has been designed. The circuit uses an 8-b flash ADC (analog-to-digital converter) running at 36 MHz and continually sampling the signal from the preamplifier or shaping amplifier. The digitized signal is then processed by a digital moving averager. A digital peak detector is used for measuring the amplitude of the shaped pulses. A novel, threshold-free circuit has been designed that combines both the moving average and peak detection functions. The circuit also provides a timing signal with an uncertainty of one sampling period. The number of the averaged samples (equivalent to the shaping time constant) is digitally controlled. The resolution of the processor is limited by the finite ADC resolution and the finite sampling frequency. Increasing the sampling frequency should improve the resolution in pulse height analysis and the timing precision. >

Digital pulse processor using moving average technique

Characteristics of a novel ring Compton scatter camera are described. This camera is designed to image medium-energy (0.5 to 3 MeV) gamma-ray fields. It consists of two position-sensitive detector arrays: a 4*4 planar array of high purity germanium (HPGe) crystals and a ring array of up to 64 NaI(Tl) crystals. Past evaluations of Compton cameras have used a planar second detector, which is subjected to a large flux of gamma rays that either pass directly through or undergo small angle scatter in the first detector. A ring array significantly reduces direct and small angle scattered events in the second detector. An analytical model for ring camera systems has been developed to predict angular resolution and efficiency, and has been benchmarked against measurements made with a prototype system consisting of the 4*4 HPGe array and an eight-element ring. Predictions are made for a system with 64 crystals in the second detector ring. >

Valentin T. Jordanov

Papers

Digital synthesis of pulse shapes in real time for high resolution radiation spectroscopy

Digital techniques for real-time pulse shaping in radiation measurements

Compact environmental anomaly sensor (CEASE): a novel spacecraft instrument for in situ measurements of environmental conditions

Digital pulse processor using moving average technique

A ring Compton scatter camera for imaging medium energy gamma rays